The process of splitting or dividing a sample into at least two representative fractional samples is used for example when a primary sample which has been taken or collected from a medium is prepared for further processing and/or analysis. The fractional samples can be subjected for example to different chemical, biological and/or physical analyses or can be further processed in different ways.
The term “primary sample” as used in the present context means any defined partial quantity which has been taken directly out of a medium. Consequently, the primary sample has the same properties as the medium at the time of taking the primary sample. Primary samples are taken for example from chemical, physical, biological, microbiological, pharmaceutical and/or food-engineering processes for analysis and/or further processing. A primary sample can further be taken from any other medium in liquid, gaseous, solid or mixed-phase form, brought into a suitable condition if desired, and subsequently analyzed. The primary sample as well as the medium can be liquid, gaseous and/or solid.
The term “sample” is used here in general for the quantity that is being split into one or more fractional samples. Accordingly, what is called a “sample” can be the primary sample as well as a processed and/or diluted primary sample.
The sample and/or the fractional samples are “representative” of the medium, which means that they have chemical and physical properties that are correlated directly with those of the medium, so that by analyzing the sample or fractional sample it is possible to determine, or at least draw conclusions about, the properties of the medium. Such a sample or fractional sample is hereinafter also referred to as “representative sample” or “representative fractional sample”.
Based on the sample or a fractional sample that originated from it, one can determine for example the composition, physical or chemical parameters of the medium or the concentration of one or more components of the medium, or keep track of the course of a reaction or of the manufacturing process of a product, to name only a few examples.
Certainly the best known of these procedures is the manual separation of an essentially uniform primary sample into two or more fractional samples that share essentially the same properties and the same composition. The individual fractional samples can contain equal or different quantities of the primary sample. Thus, the sample can be split symmetrically or asymmetrically into at least two fractional samples. In practice, a primary sample is taken out of a medium that is located in a container or in an environment; the primary sample may be bought into a suitable condition if desired and then split manually into fractional samples. Depending on the properties of the sample, the splitting into fractional samples can be performed through volumetric and/or gravimetric processes.
Besides a purely manual procedure, it is also possible to divide a sample in a partially or totally automated way. The known state of the art offers a variety of devices that are suitable for this purpose, such as for example multi-channel pipettes or volumetric and/or gravimetric dosage-dispensing systems.
Common to both the manual and the automated way of splitting a sample is the fact that the primary sample is first collected, i.e. removed from its original environment, and is split only afterwards and often under different conditions. However, this is viable especially for media which change either not at all or only insignificantly after the sample has been taken out of the medium, so that the primary sample or the fractional sample still represents a “true copy” of the medium also in the subsequent analysis and has essentially the same properties as the medium. Samples of media that change rapidly should therefore be taken and split under known conditions, for example in a glove box with controllable environmental parameters.
The splitting of a sample into a plurality of fractional samples as described above has its limitations in the splitting of small samples, with media of non-uniform composition such as for example a liquid sample with solid components, and/or if a sample is to be split essentially without changing the environment.
Problems of this kind occur for example with small production quantities and/or in the laboratory within the realm of research and development. Examples are found in the fields of process development and/or research in so-called laboratory reactors which can have reaction volumes of a few milliliters up to several liters and are quite small in comparison to process systems of a magnitude up to several ten thousand liters. When taking a sample, the latter should be as small as possible in comparison to the medium quantity that is present, while still being representative and sufficiently large for a subsequent split and analysis. Especially in cases where the reaction volumes are small, these criteria can be met only with difficulty. The taking of a sample from a container, specifically a laboratory reactor, can be accomplished for example with an apparatus and/or a method as described in US 2011/0318243 A1 or US 2011/0314900 A1, wherein a primary sample is taken, a reaction that may be currently in progress is stopped directly at the capturing element for the sample collection by adding a suitable quenching medium to the primary sample, and wherein the sample can subsequently be flushed out of the capturing element with a suitable rinsing medium. This approach for taking a sample is suitable not only for liquid samples but also in particular for media that range from liquid to viscous, for slurries, and also for some solid media of a free-flowing consistency, i.e. media consisting essentially of pourable solids. Media or samples of a non-uniform composition are also often referred to as “inhomogeneous”.
With the use of a rinse or purge medium, the volume of the sample increases in comparison to the primary sample. The primary sample is diluted. Depending on how well the primary sample mixes with the rinse medium, the primary sample and the rinse medium together can form a sample whose composition is uniform or changes over the duration of the rinsing. A sample whose composition changes over time can also come from a very fast-reacting medium and/or with continuous sample collection. A sample whose composition changes in time is hereinafter also referred to as a “time-inhomogeneous” sample.
The aforementioned manual way of splitting a sample can be used with a homogeneous sample as well as with a time-inhomogeneous sample, as the entire sample together with the rinse medium is completely removed from the environment of the medium and is further split only afterwards.
In contrast, an automated splitting of the sample into representative fractional samples can be performed in this manner only with a sample that is essentially uniform, in particular remaining uniform over time, or time-homogeneous. A time-inhomogeneous sample can thus be split only into chronologically defined fractional samples, wherein each of the fractional samples holds only a time-delimited segment of the composition of the time-inhomogeneous sample. Fractional samples of this kind occur for example when separating a sample chromatographically.
Consequently, the task presents itself to provide an apparatus as well as a method for splitting a sample, whereby a sample with a composition that varies over time can be split into two or more representative fractional samples.